US6058220A - Device for scanning an X-ray image - Google Patents

Device for scanning an X-ray image Download PDF

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Publication number
US6058220A
US6058220A US08/157,842 US15784293A US6058220A US 6058220 A US6058220 A US 6058220A US 15784293 A US15784293 A US 15784293A US 6058220 A US6058220 A US 6058220A
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United States
Prior art keywords
image
row
signal values
values
photoconductor
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US08/157,842
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Walter Hillen
Stephan Rupp
Ulrich Schiebel
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US Philips Corp
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US Philips Corp
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits
    • H04N1/409—Edge or detail enhancement; Noise or error suppression
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/30—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from X-rays

Definitions

  • the invention relates to a device for scanning a charge image which, during exposure to X-rays, is generated on a previously locally uniformly charged photoconductor as a function of the local intensity of the X-rays, using a plurality of electrometer probes which are arranged in a row and which line-wise scan the charge pattern of the photoconductor which is successively displaced in the scanning direction which extends perpendicularly to the line direction, the probes supplying for each pixel an image value which corresponds to the discharge at the relevant pixel.
  • a device of this kind is known from DE-OS 35 29 108 which corresponds to U.S. Pat. No. 4,752,944 as well as from the references cited therein.
  • the two-dimensional charge pattern which is generated on the surface of the photoconductor and which essentially corresponds to the spatial distribution of the X-ray intensity is scanned by an electrometer device.
  • the electrometer device comprises a plurality of electrometer probes which are aligned in a row. During the scanning of the charge pattern, a first line of the charge pattern is first scanned. Subsequently, the photoconductor is displaced relative to the electrometer probes, in a scanning direction extending perpendicular to the row direction, over approximately the width of one line. Subsequently, the second line is scanned. This operation is repeated until the entire charge pattern of the photoconductor has been scanned.
  • the electric signals generated during the scanning by the electrometer probes are amplified and are available for further signal processing.
  • image values are applied to an analog-to-digital converter, the converted values being stored in an image memory, there being provided a signal processor which subjects the image values of neighboring pixels of an image line to a low-pass filter function, and which subjects the image values of pixels which neighbor one another in the scanning direction to a high-pass filter function.
  • the digitized image values are stored in an image memory. After all image values have been stored, the image values of the individual pixels are processed by a signal processor.
  • the described streakiness always occurs in a direction perpendicular to the line direction, i.e. the scanning direction.
  • This streakiness in the scanning direction is eliminated in that a signal processor processes the image values of the pixels, stored in the image memory, so that neighboring pixels of an image line are subjected to a low-pass filter function, the image values of pixels which neighbor one another in the scanning direction being subjected to a high-pass filter function.
  • This procedure suitably eliminates streakiness in the image, because streakiness in the scanning direction implies a low frequency component which is caused by deviating probe sensitivities or similar phenomena and which should be eliminated as much as possible. This can be achieved by the described filter function locally performed.
  • the two filter functions also inherently influence the useful signal of the image.
  • X-ray images for medical applications contain a minimum of extensive fine structures which extend exactly and exclusively in the line or scanning direction, little relevant image information is lost.
  • the design of the filter should be adapted to the relevant field of application in order to minimize the influencing of important image information.
  • the filter functions are realized by means of the signal processor and a second image memory in that the signal values stored in the first image memory are subjected to a high-pass filter function in the line direction by means of the signal processor and are buffered in the second image memory, in that the buffered values are subjected to a low-pass filter function in the scanning direction by the signal processor and are buffered again in the second image memory, and in that after calculation of all values the values buffered in the second image memory are subtracted from the values stored in the first image memory.
  • the original image values initially stored in the first image memory are processed by the signal processor so that image values of neighboring pixels of an image line are subjected to a high-pass filter function.
  • the image values thus obtained are buffered in the second image memory.
  • the image values of pixels which neighbor one another in the scanning direction are subjected to a low-pass filter function.
  • the values thus obtained are again buffered in the second image memory, the previously buffered values being erased.
  • the values stored in the second image memory after execution of the low-pass filtering operation are subtracted from the original values stored in the first image memory.
  • the high-pass filter function is realized by means of a low-pass filter function and vice versa.
  • a low-pass filter function can be performed, after which the values thus formed are subtracted from the original values.
  • a high-pass filter function is obtained.
  • two functions are successively executed, the new values thus calculated being buffered. The values thus calculated are subtracted from the original values only after execution of both functions.
  • the sequence in which the filtering operations are performed is actually irrelevant; thus, in accordance with one version, first the filtering operation is performed in the scanning direction, followed by the filtering operation in the line direction.
  • the degree of filtering as described above can be adjusted by means of a scaling factor, that depends on the purpose or the streakiness of the image scanned. This is preferably performed in that the image values stored in the second image memory are subjected to a scaling factor prior to subtraction from the values stored in the first image memory, which scaling factor is capable of reducing said values to any desired extent, thus enabling adjustment of the filtering effect.
  • the magnitude of the scaling factor is chosen as a function of the image amplitude represented by the image values so that it is comparatively small in highly exposed image areas.
  • the scaling factor is preferably chosen in dependence on the magnitude of the image values, i.e. the image amplitude. Filtering is then reduced as the image amplitude increases.
  • the magnitude of the scaling factor is chosen in dependence on the signal variation in the vicinity of an image value so that the scaling factor is comparatively small at the area of strong signal gradients.
  • the filter functions are realized using two one-dimensional filter functions.
  • the locally executed filter functions per se represent a two-dimensional filtering operation.
  • the filtering operations are preferably performed using two one-dimensional filter functions which can be readily realised.
  • FIG. 1 shows a block diagram of a device in accordance with the invention
  • FIG. 2 shows a diagram for two one-dimensional filter functions
  • FIG. 3 shows a diagram illustrating the choice of the scaling factor as a function of the image amplitude.
  • a device as diagrammatically shown in FIG. 1 comprises a photoconductor 1 which has been uniformly charged (by means not shown in the Figure) prior to an X-ray exposure of an object 14 by X-ray system 10 and which is discharged during an X-ray exposure in dependence on the intensity of the X-rays 12 passed by object 14.
  • the rays 12 and object 14 are positioned over the photoconductor 1, the side-by-side schematic representation being only for simplicity of illustration. Following this operation, the surface of the photoconductor is locally differently discharged so that it contains a charge pattern.
  • This charge pattern is scanned by means of a plurality of electrometer probes 2.
  • a multitude of electrometer probes are provided, which probes are aligned in a row on a support 3 which is merely indicated in the Figure.
  • the photoconductor 1 is scanned, first one line of the charge pattern is scanned, i.e. all signals supplied by the probes 2 are read. This is referred to hereinafter as the line direction.
  • the photoconductor 1 is displaced, using a device which is not shown in the Figures and which is controlled by a control unit 4, relative to the probes 2 over approximately the width of one scanning line in the scanning direction. This displacement thus takes place perpendicular to the line direction which extends parallel to the support 3 for the probes 2.
  • the scan direction This is referred to hereinafter as the scan direction.
  • another line of the charge pattern present on the photoconductor 1 is scanned by the electrometer probes 2. This procedure is repeated until the entire charge pattern has been scanned.
  • the signals of the probes 2, read during the scanning operation may be first amplified (by means not shown) and then applied to an A/D converter 5.
  • the data thus digitized is written into an image memory 6.
  • the image values of all pixels are present in the image memory 6.
  • the signals supplied by the relevant probe would be higher or lower in value than the signals supplied by the other probes.
  • streakiness occurs in the scanning direction, i.e. transverse of the line direction, in an image formed by reading the signals stored in the image memory 6.
  • Such streakiness could also be caused, for example by a difference in distance between the various probes and the photoconductor 1 or by low-frequency fluctuations (noise) of the probe signals.
  • This streakiness can be at least mitigated in that the image values of neighboring pixels of an image in the line direction are subjected to a low-pass filter function.
  • the image values of pixels neighboring one another in the scanning direction are subjected to a high-pass filter function.
  • the high-pass filter function is realized by way of a low-pass filter function employing a subtraction of low-passed signals from the original digitized signals.
  • the low-pass filter function is realized by subtraction of high-pass filtered image values from the original digitized signals.
  • the high-pass filtering operation to be executed on image values of neighboring pixels in the scanning direction is performed by a low-pass filtering operation followed by subtraction performed by the signal processor 7.
  • the described locally executed filtering operation can be mathematically expressed as follows.
  • F s (z, a) is the filter function and G(k) is the scaling factor.
  • the filter function F s (z, a) can be described as follows:
  • FIG. 2 shows two of such one-dimensional filter functions by way of example.
  • both filter functions are chosen so that they either do not influence or completely suppress the image values S in the extreme cases.
  • the choice of these filter functions depends on many parameters, for example on the photoconductor used, the probes, the distance between the probes and the photoconductor, the desired revolution etc, so that no generally applicable choice can be prescribed. It appears from FIG. 2, however, that pixels which neighbor one another in the line direction are subjected to a high-pass filter function and that pixels which neighbor one another in the scanning direction are subjected to a low-pass filter function.
  • the values produced by these filtering operations are subtracted from the initial values, so that ultimately exactly the opposite filtering occurs, i.e. low-pass filtering occurs in the line direction and high-pass filtering occurs in the scanning direction which extends perpendicularly to the line direction.
  • the scaling factor G(k) can be chosen in various ways.
  • the scaling factor is defined as:
  • k can be chosen in various ways. For example, when the scaling factor is to be chosen in dependence on the image amplitude: ##EQU1##
  • k max is the maximum image amplitude.
  • the factor k increases as the image amplitude increases, so that the scaling factor G(k) decreases as the image amplitude increases, with the result that the filter values subtracted from the original image values also decrease, so that ultimately the filter effect is reduced.
  • the factor a serves for evaluating the gradient amplitude, represented by the difference, and where d takes into account the pixel distance in the line direction in which the gradient amplitude is to be taken into account.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Image Processing (AREA)
  • Apparatus For Radiation Diagnosis (AREA)
  • Facsimile Image Signal Circuits (AREA)
  • Transforming Light Signals Into Electric Signals (AREA)
  • Facsimile Scanning Arrangements (AREA)
  • Image Analysis (AREA)
US08/157,842 1990-02-28 1993-11-24 Device for scanning an X-ray image Expired - Fee Related US6058220A (en)

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US08/157,842 US6058220A (en) 1990-02-28 1993-11-24 Device for scanning an X-ray image

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE4006181A DE4006181A1 (de) 1990-02-28 1990-02-28 Anordnung zum abtasten einer roentgenaufnahme
DE4006181 1990-02-28
US66103791A 1991-02-25 1991-02-25
US08/157,842 US6058220A (en) 1990-02-28 1993-11-24 Device for scanning an X-ray image

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EP (1) EP0444737B1 (de)
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DE (2) DE4006181A1 (de)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2388196A (en) * 2001-12-07 2003-11-05 Terrence Daniel Clark Electrodynamic sensor
US20060023965A1 (en) * 2004-07-30 2006-02-02 Hewlett-Packard Development Company, L.P. Adjusting pixels by desired gains and factors
US20070183681A1 (en) * 2006-02-09 2007-08-09 Hsiang-Tsun Li Adaptive image filter for filtering image information
US8923956B2 (en) 2001-12-07 2014-12-30 The University Of Sussex Electrodynamic sensors and applications thereof
US20160071247A1 (en) * 2008-03-13 2016-03-10 Canon Kabushiki Kaisha Apparatus and method for image processing and storage medium

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4330366A1 (de) * 1993-09-08 1995-03-09 Philips Patentverwaltung Verfahren zum Erzeugen von Röntgenaufnahmen und Anordnung zur Durchführung des Verfahrens

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US4752944A (en) * 1985-08-14 1988-06-21 U.S. Philips Corporation Method and apparatus for producing an X-ray image by means of a photoconductor
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US4825297A (en) * 1986-08-29 1989-04-25 Agfa-Gevaert Aktiengesellschaft Method of and apparatus for electronic contrast enhancement of reproductions of two-dimensional transparent original images
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US4912569A (en) * 1989-01-24 1990-03-27 Eastman Kodak Company Method for thresholding an image signal
US4939759A (en) * 1988-05-19 1990-07-03 U.S. Philips Corporation Method of producing an X-ray image by means of a photoconductor, and device for performing the method
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US5003618A (en) * 1989-07-14 1991-03-26 University Of Pittsburgh Of The Commonwealth System Of Higher Education Automatic adaptive anisotropic digital filtering and biasing of digitized images

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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2388196A (en) * 2001-12-07 2003-11-05 Terrence Daniel Clark Electrodynamic sensor
US20060058694A1 (en) * 2001-12-07 2006-03-16 Clark Terence D Electrodynamic sensors and applications thereof
US7885700B2 (en) 2001-12-07 2011-02-08 The University Of Sussex Electrodynamic sensors and applications thereof
US8923956B2 (en) 2001-12-07 2014-12-30 The University Of Sussex Electrodynamic sensors and applications thereof
US20060023965A1 (en) * 2004-07-30 2006-02-02 Hewlett-Packard Development Company, L.P. Adjusting pixels by desired gains and factors
WO2006015058A3 (en) * 2004-07-30 2006-03-16 Hewlett Packard Development Co Adjusting pixels by desired gains and factors
US7426314B2 (en) 2004-07-30 2008-09-16 Hewlett-Packard Development Company, L.P. Adjusting pixels by desired gains and factors
CN100571327C (zh) * 2004-07-30 2009-12-16 惠普开发有限公司 用所希望的增益和因数调节像素的方法和系统
US20070183681A1 (en) * 2006-02-09 2007-08-09 Hsiang-Tsun Li Adaptive image filter for filtering image information
US7860334B2 (en) * 2006-02-09 2010-12-28 Qualcomm Incorporated Adaptive image filter for filtering image information
US20160071247A1 (en) * 2008-03-13 2016-03-10 Canon Kabushiki Kaisha Apparatus and method for image processing and storage medium
US10147014B2 (en) * 2008-03-13 2018-12-04 Canon Kabushiki Kaisha Apparatus and method for image processing and storage medium

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JP2962527B2 (ja) 1999-10-12
EP0444737A2 (de) 1991-09-04
JPH06103376A (ja) 1994-04-15
EP0444737B1 (de) 1995-08-16
DE59106237D1 (de) 1995-09-21
DE4006181A1 (de) 1991-08-29
EP0444737A3 (en) 1992-04-29

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